Powering an emergency lighting system

ABSTRACT

An emergency LED lighting system maintains power to an LED lighting source based on measured voltages and currents provided to the LED lighting source; rolls back or decreases power provided to an LED lighting source over time in order to increase the amount of time the battery can power the LED lighting source; executes a soft start procedure, such that the power provided to the LED lighting source is gradually ramped up during activation of the LED lighting sources; identifies a type of battery coupled to the emergency LED lighting system; cycles the emergency LED lighting system between charging mode and standby mode to reduce power consumption over a window of time; detects AC power or an absence of AC power; and/or uses a status LED to communicate information about the emergency LED lighting system with a remote device.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of Ser. No. 16/009,587 filed Jun. 15,2018, allowed, titled “Powering an Emergency Lighting System,” whichclaims priority to U.S. Prov. App. No. 62/521,588, titled “Powering anLED Emergency Lighting System” and filed on Jun. 19, 2017, both of whichare incorporated herein in their entirety. This disclosure is alsorelated to U.S. application Ser. No. 16/009,794, titled “EmergencyLighting System with Charging, Standby, and Emergency Modes ofOperation”, filed on Jun. 15, 2018 and U.S. patent application Ser. No.16/009,783, titled “Emergency Lighting System with Power Rollback andBattery Identification” filed Jun. 15, 2018, both of which areincorporated herein in their entirety.

TECHNICAL FIELD

The present disclosure relates generally to emergency lighting systemsand more specifically, but not by way of limitation, this disclosurerelates to providing approximately constant power to an emergencylighting system.

BACKGROUND

Emergency lighting includes lighting that is used for path of egressillumination upon the loss of normal AC power. Some emergency LEDlighting systems include a battery charger, a battery, and a transferswitch to energize the light source upon the loss of normal power. Someemergency LED lighting systems can use additional circuitry to convert avoltage of the battery to a voltage level suitable for the associatedlight source since LED light sources or light engines are available in awide range of voltage levels and current capabilities.

An emergency LED lighting system can implement a feed forward techniqueto maintain approximately constant power. In some aspects, the batterydischarge current can be controlled to maintain input power to a DC/DCconverter. The power to the LED source can be controlled since the DC/DCconverter losses are relatively low and do not significantly impact theoutput power. Some emergency LED lighting systems include a circuit witha flyback DC/DC converter. The leakage inductance of a flybacktransformer introduces energy losses, and additional circuitry (e.g., asnubber circuit) may be included to absorb the losses. In addition, themagnetic core of the transformer may be driven in a single direction,which can reduce the transformer utilization. The flyback design canalso have higher peak currents than some other DC/DC converter types. Itwould be advantageous to provide a constant power emergency lightingsystem that does not require a flyback converter to avoid these losses,additional circuitry, and transformer under utilization.

BRIEF DESCRIPTION OF THE FIGURES

These and other features, aspects, and advantages of the presentdisclosure are better understood when the following Detailed Descriptionis read with reference to the accompanying drawings, where:

FIG. 1 is a block diagram of an example of an emergency LED lightingsystem according to one aspect of the present disclosure.

FIG. 2 is a block diagram of an example of an emergency LED lightingsystem according to one aspect of the present disclosure

FIG. 3 is a schematic diagram of an example of a circuit for maintainingconstant power output for emergency lighting according to one aspect ofthe present disclosure.

FIG. 4 is a graph of an example of an LED characteristic curve accordingto one aspect of the present disclosure.

FIG. 5 is a schematic diagram of another example of a circuit formaintaining constant power output for emergency lighting according toone aspect of the present disclosure.

FIG. 6 is a schematic diagram of another example of a circuit formaintaining constant power output for emergency lighting according toone aspect of the present disclosure.

FIG. 7 is a schematic diagram of another example of a circuit formaintaining constant power output for emergency lighting according toone aspect of the present disclosure.

FIG. 8 is a graph of an example of power rollback of an emergency LEDlighting system according to one aspect of the present disclosure.

FIG. 9 is a graph of an example of a soft start of an emergency LEDlighting system according to one aspect of the present disclosure.

FIG. 10 is a schematic diagram of an example of a battery identificationcircuit for an emergency LED lighting system according to one aspect ofthe present disclosure.

FIG. 11 is a graph of an example of an emergency LED lighting systemcycling through charging modes and standby modes according to one aspectof the present disclosure.

FIG. 12 is a flow chart of an example of a process for reducing anaverage draw on a grid by an emergency LED lighting system according toone aspect of the present disclosure.

FIG. 13 is a schematic diagram of an example of an AC detect circuitthat includes capacitive elements according to one aspect of the presentdisclosure.

FIG. 14 is a schematic diagram of an example of an AC detect circuitwith low power consumption for coupling to an emergency LED lightingsystem according to one aspect of the present disclosure.

FIG. 15 is a flow chart of an example of a process for detecting that anemergency LED lighting system is conductively coupled to a grid using adetection circuit powered by the grid according to one aspect of thepresent disclosure.

FIG. 16 is a schematic diagram of an example of a circuit fortransmitting signals by an emergency LED lighting system to a remotedevice using a status light according to one aspect of the presentdisclosure.

FIG. 17 is a schematic diagram of an example of a circuit for anemergency LED lighting system to receive signals from a remote deviceusing a photodetector according to one aspect of the present disclosure.

DETAILED DESCRIPTION

Certain aspects and features relate to providing constant power to anemergency light emitting diode (“LED”) lighting system. An emergency LEDlighting system can power an LED lighting source using an AC powersource (e.g., AC mains power) during normal operation and using anemergency power source (e.g., a battery) during an emergency mode. Theemergency LED lighting system can include a battery charging circuit forcharging a battery during a charging mode when the AC power source isavailable. In some aspects, an emergency LED lighting system can enterthe emergency mode in response to the emergency LED lighting systembeing disconnected from the AC power source. The system may also providea test mode, which may be used to test the emergency LED lighting systemto ensure components are functioning properly even though AC power hasnot been lost.

Emergency LED lighting systems are disclosed herein that: (i) maintainapproximately constant power to the LED lighting source for a variety ofLED load voltages and throughout a battery discharge cycle; (ii) providepower rollback for conserving energy; (iii) provide a soft start foractivating the LED lighting sources; (iv) identify the type of anassociated battery; (v) provide a standby mode to reduce energyconsumption; (vi) provide a low power AC detector circuit; or (vii)provide communication with remote devices. These features can improvethe efficiency of the emergency LED lighting system and allow theemergency LED lighting system to provide steadier emergency lighting forlonger periods of time.

These illustrative examples are provided to introduce the reader to thegeneral subject matter discussed here and are not intended to limit thescope of the disclosed concepts. The following sections describe variousadditional aspects and examples with reference to the drawings in whichlike numerals indicate like elements, and directional descriptions areused to describe the illustrative examples but, like the illustrativeexamples, should not be used to limit the present disclosure.

FIG. 1 depicts an example of an emergency LED lighting system 100. Inthis example, the emergency LED lighting system 100 includes acontroller 140, a battery charger 110, a battery pack 130, and anemergency LED driver 120. During normal operation of the emergency LEDlighting system 100 (e.g., charging mode), the battery charger 110 canbe coupled by connection 102 to an AC power source (e.g., AC mainspower). The battery charger 110 can receive an AC input from the ACpower source and use the AC input to charge the battery pack 130. Thebattery charger 110 can also use the AC input to power the controller140.

Although FIG. 1 depicts the battery charger receiving the AC input anddistributing power amongst the other devices in the emergency LEDlighting system 100, other implementations are possible. For example,other types of circuits may power the emergency LED Driver 120 andcontroller 140.

The emergency LED driver 120 can include a current converter 122, acurrent controller 124, a voltage sensor 126, and a current sensor 128.The emergency LED driver 120 can direct power from the AC power sourceto an LED lighting source, via connection 152, during normal operation.The voltage sensor 126 can include a resistor divider coupled inparallel to the LED lighting source for measuring a voltage across theLED lighting source. The current sensor 128 can include a resistorcoupled in series to an output of the LED lighting source for measuringa current passing through the LED lighting source. During emergencymode, the current controller 124 and the current converter 122 providecurrent to the LED lighting source. The current controller 124 canadjust the current being provided to the LED lighting source based oninstructions from the controller 140.

The controller 140 can be communicatively coupled to the battery charger110, the emergency LED driver 120, and the battery pack 130. Thecontroller 140 can communicate with the battery charger 110 to controlwhen the battery charger 110 provides power to the battery pack 130. Thecontroller 140 can query the battery pack 130 to determine the type ofbattery pack and to monitor status of the battery. The controller 140can be coupled to the emergency LED driver 120 for instructing thecurrent controller 124 to adjust the current being provided to the LEDlighting source. For example, the controller 140 can receive the voltagefrom the voltage sensor 126 and the current from the current sensor 128,determine a power being provided to the LED lighting source based on thevoltage and the current, and instruct the current controller 124 toadjust the current provided to the LED lighting source such that apredetermined power is provided to the LED lighting source.

FIG. 2 depicts the battery charger 110, emergency LED driver 120,battery pack 130, and controller 140 of FIG. 1 used in emergency LEDlighting system 200. In this example, the emergency LED lighting system200 further includes an AC module 260, a test switch pilot light(“TSPL”) 250, a relay load transfer switch 222, and a transceiver 280.The AC module 260 includes an AC Relay 262, a surge protection circuit264, an AC detect circuit 266, and EMI filter 212. The battery charger110 includes a charger enable circuit 214, a charger controller 216, anda battery charger circuit 218. The controller 140 includes a 5 V powersupply 244, a battery disconnect 242, and a microcontroller 246.

The AC detect circuit 266 can be conductively coupled to the output ofthe surge protection circuit 264 for detecting the presence or absenceof power from the AC power source. For example, the AC detect circuit266 can detect a loss of AC power and notify the microcontroller 246such that the microcontroller 246 can enter an emergency mode. In theemergency mode the emergency LED driver 120 can provide power to an LEDlighting source, via connection 152, using the battery pack 130. Themicrocontroller 246 can determine the power being provided to the LEDlighting source using a voltage measured across the LED lighting sourceand a current measured at an output of the LED lighting source. Themicrocontroller can further provide instructions to the emergency LEDdriver 120 to adjust the current based on the power. For example, themicrocontroller 246 can detect a change in power provided to the LEDlighting source. The microcontroller 246 can instruct the emergency LEDdriver 120 to change the current provided to the LED lighting sourcesuch that the power remains substantially the same despite the change involtage. If the microcontroller determines that the voltage measuredacross the LED lighting source indicates a short or an out of range LEDlighting source (i.e., the measured voltage is inconsistent with theknown rating for the LED lighting source), then the microcontroller mayinstruct the emergency Led driver to reduce the current to the LEDlighting source.

The microcontroller 246 can instruct the battery disconnect 242 toconnect or disconnect the battery 130 from the emergency LED driver 120.During emergency mode or test mode, the battery is connected to theemergency LED driver.

When the emergency lighting system 200 is in charging mode, themicrocontroller 246 controls the battery disconnect 242 to disconnectthe battery from the emergency LED driver 120 and controls the batterycharger circuit 218, via the charger enable circuit 214, to charge thebattery 130. When the lighting system is in emergency mode, themicrocontroller 246 controls the battery disconnect 242 to connect thebattery 130 to the emergency LED driver 120 and disables the batterycharger 110. In some aspects, the emergency lighting system 200 mayinclude a standby mode. In standby mode the system uses battery powereven though AC power is available to reduce AC power consumption. Whenthe emergency lighting system 200 is in standby mode, themicrocontroller 246 can control the battery disconnect 242 to connectthe battery to the emergency LED driver and control the charger enablecircuit to disable the battery charger 110. The emergency lightingsystem 200 may cycle between charging mode and standby mode.

In some aspects, the battery 130 can be removable and modular such thata variety of different battery packs configurations or batteries can beused with the emergency LED lighting system 200. Any suitable type ofbattery may be used including, but not limited to, single-cell ormulti-cell non-rechargeable or rechargeable batteries, lithiumbatteries, alkaline batteries, or atomic batteries. The emergency LEDlighting system 200 may use batteries with a range of output voltagesand discharge rates.

In some aspects, the TSPL 250 can include an LED for providing a visualindication of the status of the emergency LED lighting system 200. Inadditional or alternative aspects, the TSPL 250 can be used tocommunicate with remote devices by blinking or flashing a signal. Thetransceiver 280 can be communicatively coupled to (or included in) themicrocontroller 246 for allowing the microcontroller 246 to communicatewith other lighting systems and lighting drivers using any suitableprotocol including, but not limited to, the LEDCODE protocol. Othertypes of transceivers and other communication protocols may also beused.

The controller 140 can include one or more processors that executecomputer-executable program code stored in a memory device, accessinformation stored in the memory device, or both. Program code mayinclude machine-executable instructions that may represent a procedure,a function, a subprogram, a program, a routine, a subroutine, a module,a software package, a class, or any combination of instructions, datastructures, or program statements. A code segment may be coupled toanother code segment or a hardware circuit by passing or receivinginformation, data, arguments, parameters, or memory contents.Information, arguments, parameters, data, etc. may be passed, forwarded,or transmitted via any suitable means including memory sharing, messagepassing, token passing, and network transmission, among others.

Examples of a processor include an application-specific integratedcircuit, a field-programmable gate array, or any other suitableprocessing device. The processor can include any number of processingdevices, including one. The processor can include or communicate withthe memory device. The memory device can store program code that, whenexecuted by the processor, causes the processor to perform theoperations described in this disclosure.

The memory can include any suitable non-transitory computer-readablemedium. The computer-readable medium can include any electronic,optical, magnetic, or other storage device capable of providing aprocessor with computer-readable program code or other program code.Non-limiting examples of a computer-readable medium include a magneticdisk, memory chip, optical storage, flash memory, storage class memory,a CD-ROM, DVD, ROM, RAM, an ASIC, magnetic tape or other magneticstorage, or any other medium from which a computer processor can readand execute program code. The program code may includeprocessor-specific program code generated by a compiler or aninterpreter from code written in any suitable computer-programminglanguage. Examples of suitable programming language include Assemblylanguage, C, C++, C #, Visual Basic, Java, Python, Perl, JavaScript,ActionScript, etc.

The microcontroller can execute program code, which can include anemergency lighting engine stored on a non-transitory computer-readablemedium. The emergency lighting engine can be executed to perform variousoperations described herein.

The operations include, but are not limited to: maintainingapproximately constant power to the LED lighting source based onmeasured voltages and currents provided to the LED lighting source;rolling back or decreasing power provided to an LED lighting source overtime in order to increase the amount of time the battery can power theLED lighting source; executing a soft start procedure, such that thepower provided to the LED lighting source is gradually ramped up duringactivation of the LED lighting sources; identifying a type of batterycoupled to the emergency LED lighting system 200; cycling the emergencyLED lighting system 200 between charging mode and standby mode to reducepower consumption over a window of time; detecting AC power or anabsence of AC power; and using a status LED to communicate informationabout the emergency LED lighting system with a remote device.

Although not depicted in FIGS. 1-2, the emergency lighting system caninclude any type of diode-based lighting sources including, but notlimited to LEDs OLEDs, qLEDs, SLEDs, laser diodes, etc. The lightingsources can include one or more devices of various types. The lightingsources can be modular and replaceable. The emergency lighting systemcan operate with different lighting sources with different operatingvoltages. The lighting sources, such as LEDs, may be arranged in series,in parallel, or any combination thereof and different types of LEDs maybe included in the same lighting system.

The number, type, and arrangement of devices depicted in FIGS. 1-2 areprovided for illustrative purposes. Additional and/or different devicesmay be used.

Providing Constant Power to an LED Light Source Using a SEPIC Converter

In some aspects, emergency LED lighting systems maintain approximatelyconstant power over a wide range of LED load voltages. The emergency LEDdrivers disclosed herein can use voltage and/or current feedback from anLED lighting source in order to maintain approximately constant power.

FIG. 3 depicts an example of an emergency LED driver 320 in an emergencyLED lighting system 300 for providing approximately constant power to anLED lighting source 380. The emergency LED lighting system 300 caninclude the emergency LED driver 320, a battery 330, a microcontroller340, and the LED lighting source 380. The emergency LED driver 320 canbe conductively coupled to the battery 330 at a first battery connectionpoint 332 and a second battery connection point 334. The emergency LEDdriver 320 can also be conductively coupled to the LED lighting source380 at a first LED lighting source connection point 382 and a second LEDlighting source connection point 384.

The emergency LED driver 320 can include a current converter 322, acurrent controller 324, a voltage sensor 326, and a current sensor 328.In one implementation, the current controller uses the TPS92690 currentcontroller provided by Texas Instruments, but other implementations mayuse other controllers or components. In this example, the currentconverter 322 includes a single-ended primary inductor converter(“SEPIC”). The SEPIC includes capacitors C1 and C2 in the DC currentpath, which can cause the current converter 322 to exhibit an inherentdegree of short circuit protection. This implementation can use twostandard inductors, L1 and L2, and does not require a customtransformer.

The voltage sensor 326 can include a resistor divider in parallel to theLED lighting source 380. In this example, the voltage sensor 326includes two resistors, R2 and R5 that are coupled in series. R2 iscoupled to the first LED lighting source connection point 382 and R5 iscoupled to the second LED lighting source connection point 384. Thevoltage at a point between the two resistors can be input to themicrocontroller 340 on the LED voltage sense line in FIG. 3. Themicrocontroller 340 can determine the voltage across the LED lightingsource 380 based on the voltage on the LED voltage sense line and theresistances of R2 and R5, which can be predetermined. The voltagebetween R2 and R5 can also be input to the current controller 324, e.g.via an input for over voltage protection.

The current sensor 328 can include a current sense resistor R11 coupledto the second LED lighting source connection point 384. The voltageacross R11 can be input to the microcontroller 340 on the LED currentsense line shown in FIG. 3. The microcontroller 340 can determine thecurrent passing through the LED lighting source 380 based on the voltageon the LED current sense line and the resistance of R11, which can bepredetermined.

The microcontroller 340 can use the LED voltage sense and LED currentsense inputs to determine the power being provided to the LED lightingsource 380. The microcontroller can also detect changes in the powerbeing provided to the LED lighting source 380. The microcontroller 340can transmit a signal to the current controller 324 to adjust thecurrent. In this example, the microcontroller 340 transmits a signal tothe current adjust input of the current controller 324. Themicrocontroller 340 can gradually adjust the voltage on the currentadjust input to instruct the current controller 324 to adjust thecurrent output by the current converter 322.

FIG. 4 depicts a graph of an example of a characteristic curve for theLED lighting source 380 in FIG. 3. The controller 140 can detect faults(e.g., short circuits and open circuits) by comparing the measuredvalues received via the LED voltage sense and LED current sense inputswith the expected values on the LED characteristic curve. For example,upon detecting a loss of AC power and entering emergency mode, themicrocontroller 340 can instruct the current controller 324 to increasethe current, from substantially zero, by ramping up the voltage outputon the current adjust line connected to the current controller 324. Inone example, the microcontroller outputs a pulse width modulated signalto adjust the current, which can be filtered to obtain an analog controllevel. Initially the microcontroller 340 can instruct the currentcontroller 324 to keep the current output by the current converter 322low while the microcontroller 340 monitors the voltage across the LEDlighting source 380 by monitoring the voltage on the LED voltage senseline.

As shown by the LED characteristic curve in FIG. 4, a voltage across theLED lighting source 380 can be present even at very low current levels(e.g., 1-5 mA). Thus, if the microcontroller 340 detects no voltage, ora voltage below a predetermined fault voltage, across the LED lightingsource 380, the microcontroller 340 can determine a short has occurred.In response to detecting the short, the microcontroller 340 can instructthe current controller 324 to reduce the current output by the currentconverter 322.

In response to the microcontroller 340 detecting a voltage across theLED lighting source 380 within a predetermined range, themicrocontroller 340 can instruct the current controller 324 to increasethe current output by the current converter 322. The microcontroller 340can continue to monitor a voltage across the LED lighting source 380 asthe current passing through the LED lighting source 380 is increased. Insome examples, the current controller 324 can continue to ramp-up thecurrent output by the current converter 322 until a predetermined powerlevel is detected by the microcontroller 340. The microcontroller 340can continue monitoring the power provided to the LED lighting source380 and instruct the current controller 324 to adjust the current outputby the current converter 322 as necessary to maintain a predeterminedpower level. In some aspects, the microcontroller 340 can determine thepower provided to the LED lighting source 380 by multiplying the voltagedetermined to be across the LED lighting source 380 by the currentdetermined to be passing through the LED lighting source 380.Additionally or alternatively, the power can be determined by a“look-up” table of corresponding current levels for given LED voltages.By monitoring the power provided to the LED lighting source 380 andinstructing the current controller 324 to adjust the current output bythe current converter 322, the power provided to the LED lighting source380 can be maintained regardless of changes in the voltage provided bythe battery as the battery 130 discharges.

In this example, the current controller 324 includes an overvoltageshutdown function. The current controller 324 can monitor the voltageprovided by the battery 130 using a resistor divider including R1 andR3. The current controller 324 can also monitor the voltage provided tothe LED lighting source 380 using the voltage sensor 326. In response todetecting a voltage from the battery 130 or across the LED lightingsource 380 that exceeds a predetermined threshold value, the currentcontroller 324 can reduce the current being output by the currentconverter 322. In additional or alternative examples, themicrocontroller 340 can detect an open-circuit condition due to thevoltage across the LED lighting source 380 exceeding the predeterminedthreshold value, or a fault voltage level, and instruct the currentcontroller 324 to reduce the current output by the current converter322.

By continuously or periodically monitoring the voltage across the LEDlighting source 380 and the current through the LED lighting source 380,the emergency LED lighting system can resume operation upon removal of adetected fault. For example, in the case of a short, the voltage acrossthe LED lighting source 380 determined by the microcontroller 340 can bevery low (e.g., below a predetermined fault voltage). Themicrocontroller 340 can instruct the current controller 324 to keep thecurrent output by the current converter 322 at a fault current level.The fault current level can be a predetermined value that is less than arange of operating current levels, which are used during an emergencymode to provide power to the LED lighting source 380. In response to thefault being removed, a voltage across the LED lighting source above thefault voltage threshold may be sensed by the microcontroller 340 and maytrigger the microcontroller to increase the current to the LED lightingsource.

In the case of an open circuit, the voltage across the LED lightingsource 380 may be above a threshold voltage or a predetermined faultvoltage. The microcontroller 340 can instruct the current controller 324to keep the current output by the current converter 322 at the faultcurrent level. When the open circuit is resolved (e.g., the LED lightingsource 380 is reconnected), the microcontroller 340 can sense a voltageacross the LED lighting source 380 within a proper range and cantransmit instructions for ramping up the current to the desiredoperating level.

Providing Constant Power to an LED Lighting Source Using a BoostConverter

FIG. 5 depicts another example of an emergency LED driver 520 includedin an emergency LED lighting system 500 for providing approximatelyconstant power to an LED lighting source 580. The emergency LED lightingsystem 500 can include the emergency LED driver 520, a battery 530, amicrocontroller 540, and the LED lighting source 580. The emergency LEDdriver also includes a voltage divider 526 and a current sense resister528. The emergency LED driver 520 can be conductively coupled to thebattery 530 at a first battery connection point 532 and a second batteryconnection point 534. The emergency LED driver 520 can also beconductively coupled to the LED lighting source 580 at a first LEDlighting source connection point 582 and a second LED lighting sourceconnection point 584.

In this example, the current converter 522 includes a boost converter.Unlike the SEPIC converter in FIG. 3, the boost converter includes no DCblocking capacitors between the battery 530 and the LED lighting source580 so the converter cannot regulate below battery voltage. To address ashort-circuit fault or a condition where the LED voltage is below thebattery voltage, the emergency LED driver 320 includes a switch Q1 inseries between the first battery connection point 532 and the currentconverter 522. The switch Q1 can be controlled by the microcontroller540 to connect and disconnect the current converter 522 from the battery530. For example, the microcontroller 540 can open Q1 and disconnect thecurrent converter 522 from the battery 530 in response to detecting thevoltage across the LED lighting source 580 is below battery voltage. Insome examples, the microcontroller can also detect a fault by detectinga current that exceeds a predetermined fault level as measured by thecurrent sensor 528. The microcontroller 540 can be configured to retryoperation by closing the switch Q1 at a periodic rate. Once the faulthas been corrected, the microcontroller can restore power to the LEDlighting source 580.

The circuits of FIGS. 3 and 5 may be used in a feed forward manner byusing battery voltage instead of LED voltage for the power calculations.If battery voltage is used, then the input power to the currentconverter is controlled. The LED power differs from the calculated powerby the amount of any converter losses.

Providing Constant Power to an LED Lighting Source Using a Transformer

Some LED lighting loads may require a higher voltage than what may beprovided by a SEPIC or boost converter. In some examples, an emergencyLED lighting system can use a transformer to provide high voltageconstant power. FIG. 6 depicts an example of an emergency LED driver 620included in an emergency LED lighting system 600 for providingapproximately constant power to an LED lighting source 680. Theemergency LED lighting system 600 can include the emergency LED driver620, a battery 630, a microcontroller 640, and the LED lighting source680. The emergency LED driver 620 can be conductively coupled to thebattery 630 at a first battery connection point 632 and a second batteryconnection point 634. The emergency LED driver 620 can also beconductively coupled to the LED lighting source 680 at a first LEDlighting source connection point 682 and a second LED lighting sourceconnection point 684.

In this example, the emergency LED driver 620 includes a transformer 690in a push-pull configuration controlled by a converter 622 that includesswitching transistors Q1 and Q2, resistor R2, and output diodes D1 andD2. The power provided to the LED lighting source 680 can be adjusted bythe current controller 624 controlling a duty cycle of the switchingtransistors Q1 and Q2. The magnetic utilization in this example is goodbecause the magnetic core is being driven in both directions. Thetransformer 690 can provide galvanic isolation between thebattery-powered low-voltage circuits and the LED lighting source 680.This separation can be beneficial since the LED lighting source 680 andthe emergency LED driver 620 may be of a high voltage configuration andmay share common connections with the LED driver circuits.

In this example, a voltage sensor 626 can be used to determine thevoltage across the LED lighting source 680. The voltage sensor 626 caninclude a divider formed by a pair of diodes coupled to opposite ends ofa transformer winding and coupled in series with a capacitor C3. Avoltage between the pair of diodes D8, D9 and the capacitor C3 can beprovided as an input to the microcontroller 640 on the LED voltage senseline. The microcontroller 640 can determine the voltage across the LEDlighting source 680 based on the voltage on the LED voltage sense lineand the capacitance of C3.

In this example, an isolated current sensor 650 can measure a voltageacross the current sense resistor 628 and output a voltage on an outputcurrent sense line connected to the microcontroller 640. Themicrocontroller can determine the current passing through the LEDlighting source 680 based on the voltage on the output current senseline.

FIG. 7 depicts another example of an emergency LED driver 720 includedin an emergency LED lighting system 700 for providing approximatelyconstant power to an LED lighting source 780. The emergency LED lightingsystem 700 can include the emergency lighting driver 720, a battery 730,a microcontroller 740, and the LED lighting source 780. The emergencyLED driver 720 can be conductively coupled to the battery 730 at a firstbattery connection point 732 and a second battery connection point 734.The emergency LED driver 720 can also be conductively coupled to the LEDlighting source 780 at a first LED lighting source connection point 782and a second LED lighting source connection point 784.

In this example, the emergency LED driver 720 includes a converter 760,a FET driver 770, a transformer 722, a voltage sense point 726, and acurrent sense point 728. Transistors Q1 and Q2 may be driven in a fullconduction period although some “dead time” may be required betweentransitions. The microcontroller 740 can control the power provided tothe LED lighting source 780 by providing control signals to the FETdriver 770 and the converter 760.

The voltage across the LED lighting source 780 and the current throughthe LED lighting source 780 can be determined by circuits on the primaryside of the transformer 722 such that additional isolated measurementtechniques are not required. In this example, the microcontroller 740can include an input for coupling to the current sense point 728. Avoltage can be induced on the current sense line by the current sensepoint 728 based on the current passing through the LED lighting source780. The microcontroller 740 can include another input for coupling toan LED voltage sense line. A voltage can be induced on the LED voltagesense line based on the voltage across the LED lighting source 780. Themicrocontroller 740 can determine the power being provided to the LEDlighting source 780 based on the voltages on the current sense line andthe LED voltage sense line.

Conserve Energy at Low Temperatures by Performing Power Rollback

In some aspects, battery performance degrades with falling temperatures.Batteries (e.g., battery 130 in FIG. 2) can be made of various chemicalcompounds including NiCd, NiMH, or LiFePO4. Batteries can also includesupercapacitors including a pair of conductors separated by aninsulator. During periods of low temperatures, an emergency LED lightingsystem can rollback or decrease an output power of an emergency LEDlighting driver in order to conserve battery life and provide emergencylighting for a predetermined minimum amount of time (e.g., 90 minutesper UL924 requirements). Generally, the colder the ambient temperature,the more degraded the performance of the battery. Therefore, in someexamples, the colder the ambient temperature, the greater the powerrollback.

The emergency LED lighting system can include or be communicativelycoupled to a temperature sensor for determining an ambient temperature.In one example, the battery pack includes a temperature sensor andprovides temperature information to the microcontroller. When the systementers emergency mode or test mode, the microcontroller may determinethe ambient temperature for the battery pack and based on thetemperature determine whether to implement power rollback. If thetemperature is beyond a predetermined value (e.g., the temperature isless than a minimum temperature), the microcontroller can control theLED driver to rollback its output power based on a band in which theambient temperature falls. Each band can be associated with atemperature range and indicate an amount of power rollback from ratedpower. Each band can include one or more rollback stages, which definean amount of time to decrease power. For example, an emergency LEDlighting system can define the following temperature bands and rollbackstages:

i) temperature > = 25° C. (no rollback) ii) 20° C. < = temperature <25°C. 3.3% (stage 1), 3.3% (stage 2) (6.6% total) iii) 15° C. < =temperature <20° C. 6.6% (stage 1), 6.6% (stage 2) (13.2% total) iv) 10°C. < = temperature <15° C. 9.9% (stage 1), 9.9% (stage 2) (19.8% total)v) 5° C. < = temperature <10° C. 13.2% (stage 1), 13.2% (stage 2) (26.4%total) vi) temperature <5° C. 16.5% (stage 1), 16.5% (stage 2) (33%total)

FIG. 8 is a graph depicting an example of power rollback by theemergency LED lighting system 100 in FIG. 1. Although FIG. 8 isdescribed in reference to the emergency LED lighting system 100 in FIG.1, power rollback can be used with other emergency LED lighting systemsor lighting systems with limited power sources. In this figure, time isnot to scale due to the illustration of actions with both short and longtime durations. Between time indicator 0 and t₁ 852, the LED drivergradually increases power to the LED lighting source from 0 to fullrated power P₁ 874. The time between 0 and time indicator t₁ 852 maycorrespond to a 10-second “soft start” further explained below. Power ismaintained at full rated power P₁ until time indicator t₂ 854. Stage 1rollback 820 begins at time indicator t₂ 854 and ends at time indicatort₃ 856. Power is decreased from full rated power P₁ 874 to a reducedpower level P₂ 872. Power is maintained at reduced power level P₂ 872until time indicator t₄ 858. Stage 2 rollback 830 begins at timeindicator t₄ 858 and ends at time indicator t₅ 860. Power is decreasedfrom reduced power level P₂ 872 to reduced power level P₃ 870. Aftertime indicator t₅ 860, power is maintained at reduced power level P₃ 870until AC power is restored, test mode is exited, or the battery pack 130is depleted and can no longer maintain emergency lighting power.

Other variations of power rollback are possible. For example, thetemperature may be considered when emergency mode or test mode isinitiated, may be considered at various points during emergency or testmode, or may be considered at each potential rollback stage. Operatingcharacteristics other than temperature may also be considered, such asthe age of the battery, the hours of operation of the battery, batterylife calculations, etc. The timing of the rollback stages and the timebetween rollback stages may differ based on temperature, operatingcharacteristic values, or other factors. The decrease in power during arollback stage may be non-linear and the amount of the decrease may bedifferent for different stages. The use of soft start is optional andnot required for power rollback.

Activating Emergency LED Lighting Source Using a Soft Start

In some aspects, an emergency LED lighting system can activate LEDlighting sources using a soft start. A soft start can include a processwhereby an emergency LED lighting driver “gently” turns on its attachedLED lighting source by gradually increasing its output current or powerat a predetermined rate over time. A soft start may be used when thesystem enters emergency mode or test mode.

FIG. 9 depicts a graph of an example of a soft start applied by theemergency LED lighting system 100. Although FIG. 9 is described inreference to the emergency LED lighting system 100 in FIG. 1, a softstart can be applied by other emergency LED lighting systems or otherbattery powered systems. During the soft start, the controller 140 caninstruct the emergency LED driver 120 to adjust its output current fromzero up to a current associated with the emergency current I₁ 910 overthe course of a short time period, 0-t₁ (e.g., 10 seconds).

In some aspects, gradually increasing the current can minimize in-rushcurrent in the circuitry components and can place less strain on thebattery pack 130 that is supplying the power, which can improve thelifespan of the battery pack 130. In additional or alternative aspects,gradually increasing the current draw from the battery pack 130 whenentering the test mode or the emergency mode can lessen the initialvoltage “droop” (especially at cold ambient temperatures) when comparedto pulling full emergency power current from the battery pack 130 whenentering emergency mode or test mode. Although FIG. 9 depicts a linearincrease in emergency output current, other non-linear implementationsof a soft start are possible.

Identifying Battery Coupled to the Emergency LED Lighting System

An emergency LED lighting system can be coupled to different types ofbattery packs. The emergency LED lighting system described herein canaccurately identify the type of battery pack and then adjust itsoperation accordingly. Exemplary adjustments may include adjustments toemergency output voltage, current and power, battery voltage ranges, aswell as battery charge current, battery charge time, and batterycapacity gauge. In some aspects, the system uses a two-resistor dividerto identify the type of battery pack. FIG. 10 depicts an example of abattery identification circuit 1000 that can be included in theemergency LED lighting system 100. Although FIG. 10 is described inreference to the emergency LED lighting system 100 in FIG. 1, otherimplementations are possible. The battery identification circuit 1000can include a resistor divider formed by resistor 1010 and resistor1020. The resistor divider can be coupled between a voltage bus 1070 andground. In one example, the voltage bus is a 5-volt bus. Resistor 1020has a known resistance and is installed on a circuit board associatedwith the system. Resistor 1010 is installed in the battery pack andidentifies the type of battery pack. Different types of battery packshave different values of resistors. The voltage 1030 between the tworesistors 1010, 1020 is provided to an analog-to-digital converter(“ADC”) 1040. A reference voltage 1050 is also provided to the ADC. Theoutput of the ADC 1040 provides a digital value that the microcontrolleruses to determine the type of battery pack. In some implementations, theADC is provided by the microcontroller and the reference voltage isgenerated within the microcontroller.

Battery packs of the same type (e.g., the same # of cells, voltage,battery chemistry, etc.) can use a resistor 1010 with the same value sothat the digital value 1060 is the same for battery packs of the sametype. In one implementation, the microcontroller uses a table todetermine the type of battery pack from the digital value.

In some aspects, the microcontroller can further determine that anunsupported battery pack or no battery pack is attached to the emergencyLED lighting system based on the digital voltage 1060. For example, ifan unsupported battery pack (e.g., without resistor 1010 or with aresistor having an unknown value) is coupled to the emergency LEDlighting system 100, the digital value 1060 will not be an expectedvalue or within an expected range of values and the system can determinethat no battery pack or an unsupported battery pack is installed.Accurately and reliably identifying the battery pack can increase thereliability of the emergency LED lighting system 100 and enhance theability of the emergency LED lighting system 100 to report possibleerror conditions to a user through either visual indication or throughother means of communications. Using the resistor divider of FIG. 10 ismore accurate than other types of battery pack identification approacheswhich attempt to identify the type of battery pack by sampling outputsof an attached battery pack over time and comparing the sampled outputswith expected outputs from a variety of different batteries.

Standby Mode to Reduce Energy Consumption

In some aspects, the energy consumption of an emergency LED lightingsystem may be adjusted so the system meets energy consumptionregulations, such as California Energy Commission (“CEC”) Title 20. Forexample, an emergency LED lighting system can enter a standby mode inresponse to detecting that the battery voltage exceeds a predeterminedvoltage. During standby mode, the emergency LED lighting system can turnoff or disable its battery charger circuit, and draw power from thebattery, thereby reducing the energy consumed from the AC mains powerduring standby mode to nearly zero. The emergency LED lighting systemcan remain in standby mode (consuming energy from the battery) until thebattery voltage decreases to a predetermined value, referred to hereinas a recharge voltage, V_(Recharge). V_(Recharge) can be selected toensure that the battery maintains sufficient energy to power the LEDlighting source for a predetermined minimum amount of time duringemergency mode. In response to the battery voltage decreasing to, orbelow, V_(Recharge), the emergency LED lighting system can enter acharging mode. In the charging mode, the emergency LED lighting systemcan turn on its battery charger circuit and charge the battery to apredetermined voltage, V_(Full). In response to the battery beingcharged to V_(Full), the emergency LED lighting system can again enterthe standby mode. In some aspects, the cycle of switching between thestandby mode and the charging mode can continue as long as power ispresent on the AC mains power. In additional or alternative aspects, thecycle can be interrupted by the emergency LED lighting system entering atest mode or an emergency mode. For example, the emergency LED lightingsystem can switch to an emergency mode in response to AC power beinglost at any time during the charging mode or standby mode.

The emergency LED lighting system can use battery characteristics otherthan voltage for determining when to enter standby mode or chargingmode. In some examples, the emergency LED lighting system can monitorcurrent, power, or stored amp-hr. In additional or alternative examples,the emergency LED lighting system can include a clock and can switchbetween standby mode and charging mode based on time. By integrating thetotal power consumed from the AC mains over time when the emergency LEDlighting system cycles between charging mode and standby mode, thesystem can meet energy consumption requirements, such as the Title 20requirements.

FIG. 11 graphically depicts an example of an emergency LED lightingsystem cycling between a charge mode 1110 and a standby mode 1120 withrespect to a battery voltage, V_(Batt) depicted over time by line 1130and charge current, I_(Charge) depicted over time by line 1140. In thisexample, line 1140 indicates that I_(Charge) has a first constant valueduring the charge mode 1110 and a second constant value during thestandby mode 1120, but I_(Charge) may have other suitable values.

FIG. 12 illustrates an example process for implementing a standby modeto reduce energy consumption of the emergency LED lighting system 100.Although FIG. 12 is described in terms of the emergency LED lightingsystem 100, the process may be implemented for reducing the energyconsumption of other emergency LED lighting systems.

In block 1210, the battery is charged using the battery charger 110. Thebattery charger 110 can be activated by the controller 140 based on thecontroller's 140 monitoring of a characteristic of the battery or anoutput of the battery pack 130. The system may remain in charge modeuntil the battery voltage reaches V_(Full), a predetermined timeinterval expires, or the system enters emergency or test mode.

In block 1220, the battery charger 110 can be disconnected from the ACpower source in response to the emergency LED lighting system 100entering standby mode. The battery provides power to run the emergencyLED lighting system 100 and thereby reduces power drawn from the ACpower source to nearly zero. The system may remain in standby mode untilthe battery voltage reaches V_(Recharge), a predetermined time intervalexpires, or the system enters emergency or test mode. If the batteryvoltage reaches V_(Recharge) or the predetermined time interval expires,the system may return to block 1210 and connect the battery charger 110to the battery to enable charging mode. If the system enters emergencyor test mode, the battery may continue to provide power to the system.In block 1230, the LED emergency driver 120 provides power to the LEDlighting source using the battery in response to the controller 140determining that the emergency LED lighting system 100 is in emergencymode or test mode.

Detecting AC Power

In some aspects, regulatory requirements for power supplies and batterychargers have significantly reduced the total allowable powerconsumption of these types of devices. In one instance the requirementis a total power level of less than 1 watt. One approach to addressthese requirements is to place the device in a low power or idle modewhen power is not required by a load. Since some emergency LED lightingsystems use an output voltage of a charger circuit to determine thepresence or absence of AC power, the charger circuit remains poweredduring idle mode. Disabling the charger circuit for these systemsdisables the emergency lighting system's ability to detect a loss of ACpower.

An emergency LED lighting system can include a separate low powercircuit to detect the presence or absence of AC power and convey thisinformation to other devices in the system. The use of a low power ACdetection circuit allows the system to reduce its total powerconsumption while still allowing the system to detect a loss of ACpower.

FIG. 13 depicts an example of an AC detection circuit 1300 that includesa capacitive element 1310. In one example, multiple capacitors (C1, C2,and C3) coupled in series form the capacitive element. The capacitiveelement is coupled between an the AC power source and opto-isolator1320. In one example the capacitance of the capacitive element is 0.22μF and the circuit provides a drive current of 10 mA for theopto-isolator 1320 at 120 volts 60 Hz. The current can increase to 23 mAat 277 volts.

The opto-isolator 1320 in the circuit depicted in FIG. 13 can have awide sensitivity range and lack a precise “trigger point” for linevoltage detection. In some examples, stray voltages can exist oncircuits that have been disabled or turned off. These stray voltages canbe at a 10-volt level or even higher depending on conductor length andproximity to other conductors and can cause voltage to be improperlydetected.

FIG. 14 is an example of another AC detection circuit 1400 that includesa DIAC semi-conductor device 1430 to provide a more precise “trigger”point and to provide hysteresis. The AC detection circuit 1400 includesthe DIAC 1430 for establishing a definite threshold and provides pulsesto the opto-coupler 1410 instead of a continuous DC level. By providingpulses to the opto-coupler 1410 the AC detection circuit 1400 canprevent unnecessary losses and decrease total standby power as comparedto circuits that provide a constant DC power to the opto-coupler 1410.The current required can be much less and the components forming theseries capacitive impedance can be much smaller. In this example, theoperating current is only 3.5 mA at 277 volts. The opto-coupler providesdielectric isolation between AC line voltage and the logic and controlcircuits and components. Resistors R1, R2, and R3 provide voltagebalance and do not significantly increase losses. Resistors R7, R8, andR9 provide surge impedance and do not significantly increase losses.

The circuit on the output side of the opto-coupler 1410 can include asingle transistor and an RC network. If pluses are present, thecapacitor C5 is discharged before it can reach the V_(be) level of thetransistor and the transistor remains “off.” If no pluses are present,the resistor R5 provides base drive for the transistor and it will be“on.” The output of the opto-isolator (AC Detect) can be provided to themicrocontroller, which determines if the emergency LED lighting systemis coupled to an active AC power source based on the presence of pulseson the AC Detect line.

In additional or alternative examples, the AC detection circuit 1400 canprovide a degree of line voltage measurement since the number of plusespresent in a given time period increases with voltage. The number ofpluses can be counted by the microcontroller in order to determine anapproximate line voltage level.

Although an opto-coupler 1410 is shown in FIG. 14, the AC detectioncircuit 1400 can be used with transformer coupling as well. Using apulse transformer in place of the opto-coupler 1410 can eliminateconcerns for sensitivity variation and possible degradation. In someaspects, the AC detection circuit 1400 depicted in FIG. 14 can be usedin other electronics, including other non-emergency LED lighting systemsand other devices powered by an AC power source.

Communicating with a User or a Remote Device

In some aspects, an emergency LED lighting system can include a testswitch pilot light (“TSPL”), which can provide an indication of thestatus of the emergency LED lighting system. In some examples, the TSPLcan include a red LED and a green LED to indicate battery charge state.In additional or alternative examples, the TSPL can include non-visiblelight sources such as infrared LEDs. The TSPL can also blink (e.g.,flash or turn on and off) at a predetermined rate or pattern tocommunicate error codes. Blinking an error code for communication with ahuman observer can require a slow blink rate (e.g., approximately 1 to 2blinks per second) such that the human observer can detect that the LEDis blinking or decipher a pattern.

In some aspects, the TSPL can blink at several thousand blinks persecond. Although this blinking rate is too fast for a human observer todecipher, the blinking can be detected and deciphered by anappropriately designed electronic receiving device placed in proximityto the TSPL. For example, a smart phone that includes a suitable sensor(e.g., an on-board camera or light sensor) could detect a TSPL blinkingat rates undetectable by humans. A software application installed on thesmart phone can decipher the blinking pattern such that the emergencyLED lighting system can communicate with the smart phone using the TSPL.The emergency LED lighting system can communicate a variety of dataincluding battery status information, including battery charge state,and system status information, including error codes.

In additional or alternative aspects, a light sensor (e.g., a photodiodeor phototransistor circuit) can be included in the emergency LEDlighting system and coupled to a processing device to allowbi-directional communication via light pulses between the emergency LEDlighting system and a remote device. In some examples, the emergency LEDlighting system can receive a request for data by the light sensordetecting a blinking light produced by a remote device. In additional oralternative examples, the emergency LED lighting system can receiveconfiguration data (e.g., operating voltages, power levels, timinginformation, parameter values, etc.), or firmware updates based on lightpulses from a smart phone, tablet, or other appropriately designeddevice.

FIG. 15 depicts an example of an LED communication circuit 1500 includedin the emergency LED lighting system 100 that can blink an LED 1510(e.g., a TSPL) for communicating with a remote device. The circuitincludes a transistor 1520, a series resistor 1540, the LED 1510, and iscontrolled by an output 1530 from the microcontroller. Themicrocontroller can control the base of the transistor 1520 to turn thetransistor on and off. In one example, the transistor 1520 is turned onwhen the microcontroller outputs a logic “high” state and the transistor1520 is turned off when the microcontroller outputs a logic “low” state.The LED 1510 turns on in response to the microcontroller's output pin1530 being set to a logic “high” state and the LED 1510 turns off inresponse to the microcontroller's output pin 1530 being set to a logic“low” state. The frequency and/or duration for each pulse of the LED1510 may represent data transmitted by the system. A receiving devicesuch as a smart phone, tablet, or other appropriately designed lightsensing device can receive and decipher the data transmitted from theemergency LED lighting system 100.

FIG. 16 depicts an example of an LED communication circuit 1600 with aphotodetector 1610 included in the emergency LED lighting system 100 forreceiving light signals from a remote device. The photodetector 1610 canbe coupled in series with a resistor 1620 to form a voltage divider. Theoutput of the voltage divider can be conductively coupled to an inputpin 1630 of the microcontroller 246. The photodetector 1610 can detectlight signals from a light source coupled to a smart phone, tablet, orother appropriately designed light pulse emitting device with a lightcommunication application. The resistance of the photodetector 1610 canchange in response to the light, which can change the output of thevoltage divider. The microcontroller 246 can receive the changes in theoutput of the voltage divider via the input pin 1630 and determine datafrom the light signals. In some examples, the photodetector 1610 can beincluded on a circuit board with the microcontroller. In additional oralternative examples, the photodetector 1610 can be integrated into aTSPL assembly.

FIG. 17 is a flow chart of an example of a process for the emergency LEDlighting system 100 performing light communication. Although the processis described in regards to the emergency LED lighting system 100,circuit 1600 and circuit 1700, other implementations are possible.Including an LED communication circuit in an emergency LED lightingsystem 100 can allow for firmware updates and tests to be performedremotely.

In block 1710, a first optical signal is received by the circuit 1700from a remote device. The remote device can include a mobile phone,table, or another light pulse emitting device. When the photodetectordetects the first optical signal, the resistance of the photodetectorcan change, which changes the voltage provided to the microcontroller.

In block 1720, the microcontroller 246 determines configuration datafrom the first optical signal. The microcontroller 246 can detect achange in a voltage on the input pin 1730 conductively coupled to thecommunication circuit 1700. The microcontroller 246 can demodulate thechanges in the voltage to determine the configuration data. In someaspects, the configuration data can indicate a change in mode. Forexample, the configuration data can instruct the microcontroller 246 toenter a test mode. In additional or alternative aspects, theconfiguration data can indicate a change in a soft start or rollbackprocedure or the values used in such procedures. For example, theconfiguration data can indicate a set of different rollback percentagesto perform based on the ambient temperature. In block 1730, themicrocontroller 246 uses the configuration data to configure theemergency LED lighting system 100. In some aspects, the microcontrollerstores the configuration data to a memory device or transmitsinstructions to the emergency LED driver 120.

In block 1740, the circuit 1600 transmits a second optical signalrepresenting a status of the emergency LED lighting system 100 to theremote device. The microcontroller 246 can vary a voltage provided tooutput pin 1630 to cause LED 1610 to flash and form the second opticalsignal. In some aspects, the microcontroller can generate the secondoptical signal to include characteristics of the battery pack 130 orcurrent configuration settings. In some implementations, thecommunications transmitted to the remote device may use the LED lightingsource instead of the TSPL.

The emergency LED lighting system may use other types of communicationto communicate with a user or a remote device. For example, FIG. 2illustrates that the microcontroller communicates via a transceiver 280,such as a LEDCODE transceiver.

The foregoing description of the examples, including illustratedexamples, of the invention has been presented only for the purpose ofillustration and description and is not intended to be exhaustive or tolimit the invention to the precise forms disclosed. Numerousmodifications, adaptations, and uses thereof will be apparent to thoseskilled in the art without departing from the scope of this invention.The illustrative examples described above are given to introduce thereader to the general subject matter discussed here and are not intendedto limit the scope of the disclosed concepts.

What is claimed is:
 1. A method comprising: detecting a loss of AC powerand entering an emergency mode; powering an emergency LED driver by abattery while in the emergency mode; and powering an LED lighting sourceby the emergency LED driver while in the emergency mode by: providingLED current to an LED lighting source by controlling a current converterof the emergency LED driver to provide an initial LED current, whereinthe current converter is coupled between a first battery connectionpoint and a first LED lighting source connection point; measuring an LEDvoltage across the LED lighting source; comparing the LED voltage topredetermined voltage range; when the LED voltage is within thepredetermined voltage range, increasing the LED current to the LEDlighting source until a predetermined power level is detected; andmaintaining the predetermined power level by: monitoring the LED voltageacross the LED lighting source and the LED current passing through theLED lighting source; determining a power level based on the monitoredLED voltage and the monitored LED current; and adjusting the LED currentto the LED lighting source to maintain the predetermined power level. 2.The method of claim 1, further comprising: when the LED voltage isoutside the predetermined voltage range, controlling the LED current tothe LED lighting source to a fault current level.
 3. The method of claim2, further comprising: while maintaining the LED current at the faultcurrent level, monitoring the LED voltage across the LED lightingsource; and when the monitored LED voltage exceeds a fault voltagethreshold, increasing the LED current above the fault current level. 4.The method of claim 1, further comprising: when the LED voltage isoutside the predetermined voltage range, disconnecting the currentconverter from the battery.
 5. The method of claim 1, furthercomprising: determining an ambient temperature associated with thebattery; and when the ambient temperature falls within a rollbacktemperature range, decreasing the LED current to a first rollbackcurrent at a first rollback time.
 6. The method of claim 5, furthercomprising: decreasing the first rollback current to a second rollbackcurrent at a second rollback time; and maintaining the second rollbackcurrent until the emergency mode is exited.
 7. A method comprising:providing, by a battery, a battery output for powering an emergency LEDlighting system during an emergency mode; providing, by a currentconverter coupled between a first battery connection point and a firstLED lighting source connection point, LED current to an LED lightingsource; measuring, by a voltage sensor, an LED voltage across the LEDlighting source; measuring, by a current sensor, the LED current passingthrough the LED lighting source; using, by a controller, the LED voltageand the LED current to determine an LED power; and controlling a currentcontroller, by the controller, to maintain the LED power during theemergency mode, wherein the controller instructs the current controllerto adjust the LED current provided by the current converter to anadjusted LED current to maintain the LED power as the battery dischargesduring the emergency mode.
 8. The method of claim 7, further comprising:detecting, by the controller, a short condition based on the LEDvoltage; and controlling the current controller, by the controller, toreduce the LED current to be below a threshold current level during theshort condition.
 9. The method of claim 7, further comprising: whenemergency mode is initiated, controlling the current controller, by thecontroller, to gradually increase the LED current from a minimal LEDcurrent level to a predetermined LED current level at a predeterminedrate.
 10. The method of claim 7, further comprising: determining abattery type, by the controller, by evaluating a battery ID signalreceived from a circuit comprising at least one component associatedwith a battery pack that includes the battery and at least one componentassociated with the emergency LED lighting system.
 11. The method ofclaim 7, further comprising: determining, by the controller, an ambienttemperature associated with the battery; and when the ambienttemperature falls within a rollback temperature range, controlling thecurrent controller, by the controller, to decrease the LED current to afirst rollback current at a first rollback time.
 12. The method of claim7, further comprising: during a charging mode, determining, by thecontroller, a charge level of the battery; when the charge level isbeyond a battery full level, controlling the emergency LED lightingsystem, by the controller, to enter a standby mode, wherein the batterypowers the controller and a battery charging circuit is disabled duringthe standby mode; monitoring, by the controller, the charge level; andwhen the charge level reaches a battery recharge level, controlling theemergency LED lighting system, by the controller, to enter the chargingmode.
 13. The method of claim 7, further comprising: communicating, bythe controller, status information for the battery or the emergency LEDlighting system to a first external device via light pulses; andreceiving, by the controller, configuration data, wherein theconfiguration data is communicated from a second external device vialight pulses.
 14. An emergency LED lighting system comprising: a firstbattery connection point configured to be coupled to a first terminal ofa battery; a second battery connection point configured to be coupled toa second terminal of the battery; a first LED lighting source connectionpoint configured to be coupled to a first terminal of an LED lightingsource; a second LED lighting source connection point configured to becoupled to a second terminal of the LED lighting source; an emergencyLED driver coupled to the first battery connection point, the secondbattery connection point, the first LED lighting source connectionpoint, and the second LED lighting source connection point, theemergency LED driver comprising: a voltage sensor for sensing an LEDvoltage across the LED lighting source and providing a first sensedvoltage based on the LED voltage; a current sensor for sensing an LEDcurrent through the LED lighting source and providing a second sensedvoltage based on the LED current; a current converter coupled betweenthe first battery connection point and the first LED lighting sourceconnection point for providing the LED current to the LED lightingsource; and a controller for controlling the current converter tocontrol the LED current through the LED lighting source to maintain LEDpower when the emergency LED lighting system is powered by the batteryin an emergency mode.
 15. The emergency LED lighting system of claim 14,wherein the voltage sensor comprises a voltage divider including a firstresistor coupled to the first LED lighting source connection point and asecond resistor and the second resistor conductively coupled between thefirst resistor and the second battery connection point, and the firstsensed voltage corresponds to a voltage between the first resistor andthe second resistor.
 16. The emergency LED lighting system of claim 14,wherein the current sensor comprises a resistor conductively coupled inseries between the second LED lighting source connection point and thesecond battery connection point.
 17. The emergency LED lighting systemof claim 14, wherein the current converter is a single-ended primaryinductor converter (“SEPIC”) or a boost converter.
 18. The emergency LEDlighting system of claim 14, wherein when emergency mode is entered, thecontroller monitors the first sensed voltage and controls the currentconverter to increase the LED current while the first sensed voltage iswithin a predetermined voltage range until the LED power reaches apredetermined power level.
 19. The emergency LED lighting system ofclaim 14, wherein when emergency mode is entered, the controllermonitors the first sensed voltage and controls the current converter toreduce the LED current when the first sensed voltage is indicative of ashort or an out of range LED lighting source.
 20. The emergency LEDlighting system of claim 14, further comprising: an AC detect circuitthat outputs a signal indicating a presence of AC input power; a batterycharging circuit; and a battery, wherein the emergency LED lightingsystem enters a standby mode based on a battery voltage and the presenceof AC input power and remains in the standby mode until the batteryvoltage reaches a battery recharge level, wherein the battery powers thecontroller and the battery charging circuit is disabled during thestandby mode.